Air compressor and cooler



March 20, 1956 Filed NOV. 3, 1952 OUTLET Rssznvom K. G. HEED 2,738,659

AIR COMPRESSOR AND COOLER 2 Sheets-Sheet 1 INVENTOR.

Karl G. Heed I26 BY 6L4, fi W6 1i;

March 20, 1956 H AIR COMPRESSOR AND COOLER 2 Sheets-Sheet 2 Filed Nov. 3, 1952 D132 NHL FUNK U530 Z- Uzi-46 nl o -bOb Jan OOQ sh HFDJOWDQ Z- 90 CUL WQJ NNDwWNHL WZDJO I yu NA w .2 ../\.sz Kw 2 R m N e H m a G l r O K United States Patent The present invention pertains to the compressing of gases and more particularly to improvements in compressors and coolers therefor.

It is a general object of the present invention to pro vide a novel compression system and apparatus for gases which is simple in construction and highly efficient in operation. i

A more detailed object of the present invention is to provide a novel gas compression system which utilizes the pulsating or modulated discharge, of a compressor for increasing the efficiency of the compressing cycle.

Another object of the invention is to'provide an improved multiple stage compressor construction having a minimum of parts and being particularly suited to permit multiple constant volume cooling of the compressed gas.

Other objects and advantages of the invention willbecome apparent as the description proceeds and in view of the accompanying drawings, in which:

Figure 1 is a vertical sectional view of a two stage gas compressor and cooler system which illustratively embodies the present invention.

Fig. 2 is an exemplary temperature diagram showing the condition of the gas in various stages, of the compressing and cooling operation.

Fig. 3 is a horizontal sectional view of the cooler taken along line 3-3 in Fig. 1.

'ice j 2 T'he low pressure piston 14 is of the well known skirted type having an upper working face 18 and sealing rings 19. The piston 14 is reciprocatingly actuated in the conventional manner by means of a connecting rod 20 and crankshaft 21. Any suitable source of power, not

shown, maybe used to drive the crankshaft. I

In accordance with one of the salient features of the present invention, means are provided for utilizing the Fig. 4 is a diagrammatic view of a modified construction showing an alternative coolerconstruction.

Fig. 5 is an exemplary pressure-volume .diagram for the modified construction.

While the invention is susceptible of variousmodifications and alternative constructions, I have shown in the drawings and will herein describe in detail the preferred embodiments, but it is to be understood that I do not thereby intend to limit the invention to the specific forms disclosed, but, intend to cover all modifications spirit and scopeof the invention asyexpressed i th pended claims. 7

Referring more particularly to the drawings, Fig. 1

shows an illustrative gas compression system embodying and alternative constructions and uses falling within the the present invention. The apparatus making. up the l i system includes a gas compressor 10 providing a med ulated orpulsating output of compressed gas and :a gas cooler 11. A modulated or pulsating flow of gas as used in the present description, refers to a flow of gas which is a series of discrete masses of gas separated from each other by eithera stoppage of the gas flow or a substantial change in the pressure for a short interval of time.

. pressure stage. :1 'The high pressure piston is constructed with closed variations in pressure of the gas entrapped in thelow pressure cylinder for actuating the high pressure stage of 'thejcompressor. For this purpose, the high pressure cylinder 13 has its lower or abutting end open to the interior of the low pressure cylinder 12, forming a small diameter, co-axial extension of the latter. A'cylinder head 22'is bolted to the upper end of the high pressure cylinden e nclosing the compression chamber of the high upper and lower end faces 23, 24, respectively, to permit the application of a gas pressure to either end of the piston. The upper end face 23 acts upon gas entrapped in the high pressure cylinder 13 to compress this entrapped gas from the intake pressure to a final high discharge pressure. A pair of sealing rings 25 is provided adjacent the upper end of the high pressure piston 15 to prevent this entrapped gas from escaping past the sides of the piston. The lower end face 24 of the high pressure piston 15 is in communication with the gas pressure in the low pressure cylinder 12 since the inner end of the high pressure cylinder 13 is open to the latter. Consequently, the high pressure piston 15 is subjected to an upward force resulting from the gas pressure in the low pressure cylinder and a downward force resulting from the gas pressure in the high pressure cylinder. As the piston 15 is freely slidable in the high pressure cylinder, it will shift longitudinally therein to seek a balance between the resultant of these opposed forces and external forces axially applied to the piston.

Ina two stage compressor, it is desired to compress the gas entrapped in the second or high pressure stage from an initial pressure substantially equal to the discharge pressure of the first stage to a considerably higher final pressure. To obtain this desired high pressure output from the second stage, means are provided for applying an auxiliary upward force to the high pressure piston 15. For this purpose the high pressure piston is resiliently loaded in the direction of its compression stroke. The resilient loading is provided by a compression coil spring 26 mounted on the outer face of the cylinder head 22 in axial alinement with high pressure cylinder' 13. A tensile rod or connector 27 securely attached to the high pressure piston 15 extendsupwardly therefrom through an airtight seal 29 in the cylinder head to the free or outer end of the spring 26. A spring retainer 30, shaped to engage the outer end of the spring, is positioned on the projecting end portion of the tensile rod 27. Holding the retainer 30in any position se lected to apply the desired resilient force to the high pressure piston 15 is an adjusting nut 31 engaging the threaded end portion of the tensile rod.

The magnitude of the auxiliary upward force to be applied to the high pressure piston 15 may be readily determined from the physical dimensions of the compressor and the intake pressures of the two compressor stages. In general the maximum amount of external force which can be applied to the high pressure piston is limited by the force available to move the high pressure piston downwardly in its suction or intake stroke. This downward force is the result of the diiference between the intake gas pressures of the first and second, stages of the compressor. It may be calculated by multiplying the upper end area 23 of the high pressure piston by the difference in intake pressures in the high and low pressure cylinders 12, 13. The intake pressure of the low pressure cylinder will be approximately atmospheric pressure. As will be shown, that of the high pressure cylinder in the present system will be substantially the same magnitude as the discharge pressure of the first stage.

7 In the'illustrated compressor 1% the spring retainer is adjusted relative to the tensile rod 27 to provide a resilient upward force on the high pressure piston equal to the above mentioned downward force when the latter is in its lowest position. With the spring construction shown in Fig. 1 the upward resilient force on the high pressure piston will, of course, decrease a came aman as the high pressure piston moves upwardly. This decrease will be equal to the product of the elastic constant of the spring and the stroke of the high pressure piston. The discharge pressure of the second stage of the compressor will be the discharge pressure of the first stage plus the spring 'force on the high pressure piston at its -top position divided by the upper end area 23 of the piston. The desired size and elastic constant of the coil spring 261can therefore be determined for a desired discharge pressure of the second stage, knowing the desired size and pressures of the low and high pressure stages of the compressor.

In many instances, the spring will 'be a satisfactory means of providing this upward force, notwithstanding the variation i'n'force due to the elastic constant of the spring. If desired, a more precise loading means may be'usedto provide a more constant upward forcethroughout the stroke of the high pressure piston, such as a constant'foreeresilient linkage or a hydraulic loading means. It is desirable in accordance with accepted compressor "design to keep the residual volume or clearance of the compressor cylinders at a minimum. In the preferred embodiment of the invention, this is accomplished by making the length of the high pressure piston 15 substantially the same as the length of the high pressure cylinder 13. With this relationship between the high pressure cylinder 13 and the piston 15, the lowerend face 2i4 of'the' piston is flush with the top of low pressure cylinderlZ when the piston is in its upper limit position. Thus,there is'substantially no volume left in the low pressure cylinder 12 that is not swept by the low pressure piston. To further minimize the clearance volume, the high pressure piston 15 has an auxiliary sealing ring 32 positioned "midway of its length to limit the gas volume alongside the high pressure piston in communication with 'thelo'w pressure cylinder. 7

To provide continuous operation of the compressor 10, 'means'are provided for controlling the flowof gas into and out of the respective cylinders of the compressor. For this pur'posethe lo"-v pressure cylinder 12 is provided withan intake fitting 33 and a discharge fitting 34 securely fastenedto the outer surface of thecylinder side wallas by cap screws. The intake fitting 33 defines a gas passageway 36 alined at its inner end with an intake port37 in the'wall of the low pressure cylinder 12ndjacent the upper end thereof. The outer endof the'in 'takefitting 33 is'adapted' to receive an intake pipe or conduit 38 which may be in communication'with a source 'ofthegas to be compressed. In the alternativq the conduit 38 can be connected, if desired, to the ekhaust of a mechanism utilizing the compressed gas discharged by :the compressor to form a closed system such, for exampie;as a refrigeration system. Assembled on the inner end of the intake fitting 33 is a gas check valve 40"of the well-known spring loaded type for permitting flow 'of intake gas into the low pressure cylinder during the suction'stroke of the piston 14- and for blocking the outward flow of gas during the compression stroke.

The discharge fitting 34 for the low pressure cylinder 1's of-similar construction to that of the intakefitting,

having a gas passageway 43 alined at its'inner eiid with a discharge port 44 in the lower end portion of the wall of the high pressure cylinder. Preferably a lateral projection 45 integral with the cylinder wall is formed about the discharge port 44 to provide sufiicient clearance for the discharge fitting. A discharge valve 46 of the spring loaded disk type is positioned to cover the discharge port 44. The valve 46 is arranged to open under discharge pressure of the low pressure cylinder but to close when such pressure is lowered, as on the suction stroke of the piston'14.

Since the lower end section of the high pressure cylinder lies adjacent the discharge port 44, an auxiliary paw sageway 47 is formed in the side of the high pressure piston 15 leading from the portion of the Piston opposite the discharge port downwardly to the bottom face of the piston. The auxiliary passageway 47 is formed simply by longitudinally grooving or channeling the lower end portion of the high pressure piston. The groove or channel can be of such length as to uncover the discharge port only after the high pressure piston 15 has reached its uppermost position, or the passageway can be extended slightly in length to permit discharge of compressed gas at some earlier position of the high pressure piston in its upward travel.

Intake and discharge passageways 48, 49 for the high pressure cylinder are formed in the cylinder head 22. In the illustrated construction, the passageways 48, 49 are of generally l. shape leading upwardly from the inner faceof the cylinder head and then outwardly to the sides of'the latter. The outer end of the intake passageway 48 is adapted to receive an interstage intake pipe or conduit 50 which in the present instance is in communication with the discharge of the low pressure cylinder through an intermediate reservoir 51 and section of the cooler 11. The outer end of the discharge passageway 49 is similarly adapted to receive a discharge pipe or conduit 52 which is shown connected to a section of the gas cooler '11. An intake valve 53 and a discharge valve '54 are'provided in the respective passageways 43, 49. These valves 53, 54 are respectively similar in construction and operation to the previously described intake and discharge valves 40, 46 of the low pressure cylinder 12.

Briefly summarizing the operation of the compressor, the power operated crankshaft 21 through the connecting rod 20 reciprocates the low pressure piston 14 which upon its downward or'suction stroke causes the discharge valve 46 to close and the intake valve 40 to open permitting low pressure gas to enter the cylinder 12. The high pres sure piston 15 is now forced downwardly due to the intake gas pressure acting on its top face and the lower gas pressure of the low pressure cylinder intake acting on its bottom face. The high pressure piston continues to follow the low pressure piston downwardly until the downward force due to the abovementioned differential 'in'pr'essure equals the increasing resilient force of the compression spring 25, or until downward movement of the piston 15 is positively stopped by a mechanical abutand thus permitting the compression spring 26 to force 'the high-pressure piston upwardly. Whcn the high pressure piston has compressed the gas in'the high pressure cylinder "to its discharge pressure, the discharge valve 54 opens p'erm'itting the compressed gas to be discharged.

"At thesa'me time the high pressure piston moves upwardly "toapoi'nt where the low pressure discharge port 44 is uncovered permitting the gas compressed in the low pressure cylinder to be discharged through the outlet valve "46 when the; pressure in the low pressure cylinder reaches the'interme'diate pressure of the reservoir 51 and cooler 11. The compressed gas discharged by the low-pressure of the compression system is utilized to provide highly efiicient cooling and recompression ofthe gas. For this purpose cooling means are utilized which provide constant volume cooling of selected masses of gas In the preferred embodiment of the invention, the cooler 11 is of cylindrical shape, formed by cylindrical or tubular walls 60. The cooler walls are of double construction to define aninteriorycavity 61 through which cooling water maybe circulated; .The cooling water for the water outlet 64 forthe' cooling water is provided adjacent the upper end of the outer cooler walli l The ends of the cooler areenclos'ed by closely fitting circular coverplates 66, 67. The lower plate 66 is inserted through the top of the cooler'and rests on an internal flange 68 adjacent the lower end of the cooler. A lower retainer. plate 69 is positioned against the bottom face of the flange 68. Screws 70 passing through the retainer plate and engaging threaded holes in the lower cover plate 66, firmly clamp the two plates to the internal flange 68 in sealing contact.

The upper cover plate 67 has ag relieved rim portion which overlies the top end of the cooler walls and is clamped in position by a top retainer plate 72 and retainer ring 73. The ring is .of the expandable type having an internal tongue 74 which engagesa mating groove in the outer face of thecooler wall. The top retainer plate 72 bears against the cover plate 67 and presses itinto sealing contact with the end of the cooler walls as by means formed in an external fitting 96. 'The interstage conduit 50 is coupled to the outer end of the gas passageway 95 and conducts the cooled and compressed gas from the lower intercooler chamber 78 to the intermediate gas reservoir 51 and thence to the intake passageway of 'the high pressure cylinder 13. M 1 I Theuppermost or aftercooler chamber 76 is in communication with the discharge of the highpressure cylinder 13 by means of the-short gas conduit 52and'an' intake port 101 in the cooler wall-adjacent the top thereof. A discharge port 102 in the aftercooler Wall immediately above the upper partition 80 and an'external fittingx103 having a gas passageway 105 .conduct the gas from the aftercooler 76.-to the discharge conduit 85.

, Means are provided for each of the units of the 'comprcssion system to maintain the gas entrapped in each cooler chamber at constant volume during the cooling of the gas. The check valves 46, 54 at the outlets of the low and high compression cylinders 12, 13 respectively block the rearward flow of gas from the first intercooler chamber 77 and the aftercooler chamber 76. Spring loaded check valves 188, 169, 110 are fitted in the discharge gas of cap screws 75 which draw the retainer plate and ring together.

a The interior of the cooler .11is divided by partitions 8t), 81 into three tandem coolingchambers 76, 77, 78. The partitions are fashioned as disks fitted into close peripheral engagement with the interior cooler walls and held imposition by collapsible positioning rings 82, 83. These rings are. inserted into the cooler in collapsed condition and allowed to expand resiliently into internal grooves or notches formed in the cooler walls. Internally extending ledges on the lower edges of the positioning rings support thepartitions. Preferably the partitions 8%, 81 are a press fit into the positioning rings to ensure permanent gastight construction.

In the exemplary compression system shown in the drawings, the cooler 11 has both an intercooler section and an aftercooler section. The lowertwo cooler chambers 77, 78 together comprise the intercoolersection for the compressed gas discharged by the low pressure cylinder 12 and in turn delivered to.'the intake of the high pres-j. 1 sure cylinder 13. The top cooler chamber 76 comprises the aftercooler section for the compressed gas discharged by the high pressure cylinder 13 and delivered in turn 8 to an outlet conduit or pipe 85.?"

The individual cooling chambers are constructed to minimize the mixing of incoming'and outg'oing'gas. For this purpose, the central cooler chamber 77 has an intake port 86 adjacent its upper end. A short conduit 87 conducts the gas discharged from the low pressure cylinder discharge fitting 34 to the intake port 86. A fitting 89 having a gas passageway 90 is mounted on the outer wall of the cooler to extend a short distance to both sides of the lower partition 81. The passageway 90 communicates at one end with an outlet port 91 leading from the lower portion of the central cooler chamber 77 and at its other end with an inlet port 92'leadingto the upper portion of the bottom chamber 78. i

The lower portion of the bottom chamber 78 also has an outlet port 94 which leads to a gas passageway 95 passageways 90, 95, 105, respectively, leading from each of the cooler chambers. These discharge valves 108, 109, 110 are mounted to permit gas flow outwardly from the cooler chambers but prevent retrograde flow into the chambers.

.In accordance with the present invention, each of the cooling chambers is constructed to receive and cool a single complete pulse or modulation of the gas being compressed. Thus the volume of each cooling chamber is equal to the volume of the gas discharged by the preceding unit of the system. The first intercooler chamber 77 therefore has a volume equal to the volume of the gas discharged from the low pressure cylinder 12 by each compression stroke of the piston 14 at the discharge conditions of temperature and pressure. The volume of the aftercooler chamber 76 similarly corresponds to the volume of gas discharged from the high pressure cylinder13 on each compression stroke of the piston 15. The second intercooler chamber 78 has a volume equal to the volume of gas which has been entrapped and cooled in the chamber 77 after the same has been recomp ressed to the original discharge pressure of the low pressure cylinder 12. It will be understood that the volume of the respective chambers includes the volume of the communicating passages leading from their respective valves. in the illustrated embodiment of the invention, the construction of the compressor and cooler advantageously keeps these passages to a minimum volume.

The respective volumes of the cooling chambers 76, 77 78, as well as the corresponding sizes of the low and high pressure cylinders 12, 13, may be determined for a given set of starting and end conditions. 1 The well-known gas laws commonly used for gas compressors may be used for this purpose, or published tables and graphs of gas prop- 1 dynamic propertiesiof air, found in published gas. compressor handbooks and texts, will demonstrate'the inanner in which the respective volumes'may be determined. Fig. 2 of the drawings shows such a graph, omitting certain curves and values not needed for the present example. Briefiy described, the horizontal axis of the graph of Fig. 2 represents the volumes per pound of gas. Curves sloping gradually upward toward the right represent constant temperature. The curves sloping steeply upwardtoward the right are constant pressure lines, while those sloping downwardly toward the right are constant entropy lines, representing adiabatic gas compression or expansion.

In the present example, shown in Fig. 2, the starting conditions, indicated by the letter 'A, for the gas are atmospheric pressure and F. It will be appreciated that any-beginning weight of air or gas may be used depending .on the desired capacity of the compression system. In the present instance, one pound of air will be used for convenience, and as shown in Fig. 2 has a volnmesof 14.8 cubic feet at the starting conditions.

The selected discharge pressure of the lower pressure stage is shown as 200 pounds per square inch absolute. Since the compression of gas in the usual compressor, even with cooled cylinder walls is very nearly adiabatic, the'graphic representative of the compression of the gas is along a constant entropy line. This is represented by the straight line AB. The point, indicated by the letter B, gives the discharge volume, and temperature of the gas discharged by the low pressure cylinder 12 on each piston stroke. Therefore the first chamber 77 of the intercooler will have the volume indicated by this point B. which volume is shown to be 2.2 cubic feet for each pound of air compressed by the low pressure stage of the coinpressor.

The volume of the second intercooler stage may now be determined, and is shown by .the volume of the point D on the chart, which is 1.3 cubic feet per pound of air. Point D is readily found since the mass of gas, being isolated in the first chamber 77, cools at constant volume to substantially the temperature of the cooling water. Inthe example, the gas is shown cooled to a temperature of 100 P. which is represented by theconstant volume line BC, drawn downwardly until the 100 temperature curve is intersected. Upon entry of a new charge or pulse of into the first intcrcooler chamber 77, the .charge of gas already there will again be compressed and forced into the second intercooler chamber 78 through the passageway9il and its check valve 108. This second compression will also be adiabatic, and is graphically illustrated by the line CD, drawn on a constant entropy line upwardly toward the left to the intersection with the 200 pound per square inch pressurecurve.

After entry of the gas into the second intercooler, chamber 73, it is recoolcd at a constant volume to 100 F. by the cooling water. This cooling is shown by the vertical line D-E drawn in the same manner as the line BC. Upon another cycle or stroke of the lower pressure piston, the mass of air entrapped in the second intercooler chamber is again compressed to about 200 pounds per square inch and is forced out of the second chamber 73 through the interstage conduit 51) into the reservoir 51. This reservoir is of sufiiciently great capacity that its internal pressure is not substantially varied by the introduction therein of the individual masses of air expelled from the intercoolcr by 'the low pressure piston 14. This third com gas pression of an individual mass of air just prior to its introduction into the reservoir is shown by the constant entropy line E-F. When contained within the reservoir 51 each individual air charge occupies a pro rata volume of 1.1 cubic feet. From this reservoir the partially compressed air is introduced into the high pressure cylinder 13 without any substantial loss in pressure. Thus, in order for the high pressure cylinder to withdraw the partially compressed air from the reservoir 51 at the same rate it is charged therein from the intercooler, this cylinder is dimensioned to have a cyclic intake equal in volume to the volumetric displacement of the individual masses of air charged into the reservoir, in this instance 1.1 cubic feet.

The graphical representation of the compression of a mass of air in the high pressure stage in the illustrative case is shown by the lines F-G, G-I-1, and I-I-J. of Fig. 2. The thermodynamic action on the gas in this stage is similar to that in the low pressure stage and need not be described in detail. Suifice it to say that the line FG represents the adiabatic compression in the high pressure cylinder 13 to the final pressure of 500 pounds per square inch. The volume of a mass ofgas at point G, 0.56 cubic foot per pound in this instance, determines the'volume of the aftercooler chamber 76 which .is designed to be equal tothis gas volume. The vertical line GI-I represents the constant volume cooling in the aftercooler chamber, while the line H] shows the recompression of the gas in the aftercooler chamber 76 to the final discharge pressure, 500 pounds per square inch at which pressure it is discharged from the aftercooler.

To further insure constant volume cooling of the gas in the coolingchamber, means are provided to cool the gas quickly and efiectively during a selected interval of time. For best operation, the gas charge completely enters the cooling chamber before the gas is cooled by a substantial amount. To accomplish the latter, means are provided for synchronizing the cooling of the pulses of gas with the movement of the gas into the cooling chamber. In the illustrated construction, a stationary alined series of spaced semicircular fins 112 extend horizontally inward from the inner wall of the cooler 11 (see Figs. 1 and 3). A second alined set of spaced semicircular fins 113 is mounted horizontally in the cooler for bodily movement around the central axis of the cooler. The individual members of the two sets of fins 112, 113 are alternately spaced permitting the movable set to swing a half turn into alinement with the stationary set. Preferably the fins are accurately and closely spaced leaving but little gas space between their fiat, side surfaces when in the alined position.

The stationary fins 1-12 are cooled by contact with the inner wall of the cooler 11 to permit heat to be transferred from them to cooling water flowing through the cavity 6'1 in the cooler walls .69. The movable fins are cooled by water flowing through the center of a hollow fin supporting spindle or shaft 115. The support spindle 115 is mounted for rotation in gas tight bearings 116, 117 positioned centrally of the cooler end cover plates 66, 67. Cooling water is conducted by a pipe 118 to the interior of a sleeve 119 surrounding the lower projecting end portion of the supporting spindle 115. Radial holes or perforations 120 in the projecting portion of the spindle 115 permit the cooling water to flow into the hollow inside of the spindle. The outer end of the sleeve 119 is provided with apacking gland 122, to prevent the escape of water from the sleeve. The upper or inner end of the sleeve 119 has a flange 123 firmly mounted to the lower retainer plate 69 to hold the sleeve in position and to provide a watertight seal for its inner end. Surrounding the upper end portion of the spindle 115 which projects above-the top retainer plate 72 of the cooler is a spaced cap fitting 124 attached to the top of the cooler. An outlet opening in the cap 124 allows the cooling water to be discharged from the open end of the fin supporting spindle 115.

It will the apparent that with the two sets of cooling fins 11-2, 113 in a closed or interleaved position, comparatively little cooling of gas in the respective cooling chambers will-take place. This therefore is the position of-theplates during the entry and discharge of gas from the cooling chambers. Rotation of the movable fins 113 by a half turn of the spindle 115 into the open or nonalined position oflfers maximumcooling area and agitation of the gas for rapid cooling. The open position of the cooling fins occurs during the interval of time between pulsations or modulations of the gas by the compressor 10.

In the present embodiment the rotation of the spindle 115 is derived from movement of the compressor crankshaft 21 by means ofagear box 126 and bevel gears 127. The gears are arranged to rotate'the fins 113 into closed position for at least the latter part of the compression stroke of the pistons 14, 15 when gas is being discharged to the cooler 11. The fins are rotated to open position on the'downward or suction stroke of the pistons. If desired a Geneva movement type of gearing may be used for more rapid movementof the cooling fins into full open and closed positions. The preferred construction of the compressor in side by side relation with the cooler, permits the use of a single-fin supporting spindle readily, synchronized with the strokes of both high and low pressure pising chambers may be used as aftercoolers to give operational: characteristics comparable to multistage compressors with a minimum of parts and withhigh efficiency. A modified pump and cooler construction embodying the present invention is shown diagrammatically in Fig. 4.

of the drawings. In this instance, the cooler comprises a series of cooling chambers 201, 202,- 203, 204, arranged along the length of a conventional compressor cylinder 206, having a reciprocably drivenpiston 207. Intake tothe cylinder 206 is controlled by a spring loaded intake valye 208 located in an intake passage 209 in the head of the cy1inden; The cooling chambers have individual gas inlet conduits 201a, 202a, 203a, 204a, leading to axially spaced ports in the wall of the cylinder 2&6 for receiving hot compressed gas from the compressor, and also H have interconnecting gas conduits 211., 212, 213 permitting cooled gas to flow sequentially from chamber to chamber. Cooling of the gas in each chamber may be accomplished in any convenient manner, e; g. a water jacket or cooling coil 214. V I

The hot compressed gas received in each chamber from the cylinder is maintained at constant volume during cooling by means of check valves 215', 216 located, re spectively, in the inlet conduits to each chamber and in the interconnectingconduits 211, 212, 213. The valves 215, 216 are arranged to permit flow of gas from-the cylinder into the chambers and from chamber to chamber in the direction of the highest pressure chamber 204, but not in reverse. The highest pressure chamber 204 is provided with an outlet conduit 218 and a check valve 219 therein for discharging the compressed and cooled gas into a reservoir, or supply line.

In operatiomthe piston 207 proceeds from right to left on its compression stroke, first filling the right handor ]1owe'st pressure chamber 201 with hot compressed gas 'ata relatively low pressure. The succeeding chambers 202, 203, 204 are filled in turn with hot compressed gas at progressively higher pressures. As each chamber is filled with a fresh charge of hot compressed gas, the entire charge of cooled gas already in the chamber is forcedinto the next succeeding chamber by the incoming hot gas; T permit the cooled gas to beforced from chamber to chamber, the inlet check valves 215"may be resiliently loaded bysprings 221 to open at predetermined pressures of mechanically operated to open, only after the piston 207 has passed the port of the preceding chamher; This permits the cylinder pressure to establish a pressure differential between adjacent chambers causing the desired sequential flow of cooled gas. Any pressure differential between adjacent chambers would otherwise be neutralized by cylinder gas pressure acting through the inlet conduit of the next following chamber.

The size and axial spacing of the ports for the cool,- ing"charnbe rs may be readily calculated with the aid of the well known pressure-volume diagram, illustrated in a Fig. 5." The pressure-volume diagram has both the actual compression (indicator) curve PWh of the compressor, and an isothermal curve PN based on the particular gas being compressed and the characteristics of the com pres'sor.

One method of computing the dimensions of the cooler arrangement is as follows. First, the high and low pressures, that is, hot and cold gas pressures, for each chamher are determined. Starting with the last chamber in the series, 204, its high pressure will be equal to the output pressure of the compressor Wh. Its low pressure W1 is the point of intersection between a vertical projection fromthe point Wh, representing the compressordischarge pressure and volume, and the isothermal curve PN. In order to obtain sequential flow of cooled gas from the preceding V 10 chamber 203 intochamber 204, the high pressure of chamber-203must lie within the pressure range of chamber 204, preferably the mean pressure Wm. Starting with a point Xh on the indicator curve equal to the mean pressure Wm of chamber 204, a vertical projection to the isothermal curve gives the low pressure XI of the chamher 203. This procedure is followed for the remaining chambers, the. high pressure of each being equal to the mean pressure of the followingchamber, giving pressures Yh, Yl for chamber 202, and Zh, Zl for chamber 201. The cooling chambers have a volume relative to each other such that when the entire charge of cooled gas of 'Oneisaddedto the, cooled gas chargevin the following chamber, the pressure in the latter chamber is raised to the highest entering pressure of hot gas in the first chamber. Aclose approximation of the ratio of volumes to accomplish this may be determined directly from the illustrative curves, by equating the percentage volumere- I maining in. one chamber after cooling to the percentage volume decrease in the following chamber, assuming for this purpose constant pressure cooling at the highest pressure of the. first chamber (the mean pressure of the fol abovein terms of chamber lowing chamber). Thus from the diagram for cooling chambers 203 and 204:

A similar ratio can be worked out between the volumes of chambers 203 and 202, and chambers 202 and 201. These ratios, of course, can all be reduced to a common denominator which for convenience may be the volume of chamber 204 giving the volumes of the preceding chambers a's progressively smaller fractions of the volume of chamber 204, e. g. Vol.2oa=a. Velma; VoI.2o2= 1. V0l.2o4; V0l.2o1=c. V0l.2o4.

Both theabsolute volumes of the chambers and the spacing of their intake ports alongthe cylinder can now be calculated from the weight of hot gas each receives from the cylinder. The weight of gas in a given volume is the'product of the volume times the density of the gas. For present calculations, either the absolute densities of the gas may be used or relative densities. The latter equals the number of times the gas is compressed before entering a given chamber. Taking the intake density of the cylinder as one, for example, the density of chamber 204 equals volume P on the diagram divided by volume Wh,

For absolute volumes of the chambers, the total weight of gas received by all chambers is equated to the total weight of gas in the cylinder. This allows the entire charge or weight of gas in the cylinder to bereceived by the chambers on each piston stroke. This is represented by the following equation, in which P is the pump displacement, and dis the gas density:

The"relative"'volumes of all chambers were determined 204'and these ratios'may be' substitutedyinthe'above equation giving the absolute volume-of cham'ber'204.

,, Vol. PXd,

The absolute volumes of the remaining chambers are now the above determined ratios of the absolute volume of chamber 204.

In calculating the spacing of the ports for the chamber, it is apparent that the weight of gas in the unswept volume of the cylinder at the moment the piston passes any inlet port must be equal to the weight of gas to be Thus chamber 204, which is the last chamber, is at the head of the cylinder, there being no more chambers to receive gas from the cylinder. "However, as the piston passes the port for chamber 203, the weight of gas remaining in the cylinder is equal tothe weight of gas to be received by the following chamber 204. Since the density of gas in the cylinder at that moment is equal to that in chamber 203, its weight is the unswept volume of the cylinder times dzos. Thus:

Vol. of unswcpt cylinder d VOl-gm X g'l' 9 -203 Xi'an? For chamber 201, the total of the weights received'by chambers 202, 203 and 204 is used in the equation.

It will be apparent that the results from the above example should be modified slightly to take into account the factors for inertia and friction of the gas entering and leaving the chambers. The overall indicator .Curve for the cooler will approximate the curve MN of Fig. 5, with a saving of power represented by the area M-Wh-N.

Having thus calculated the size and axial spacing of the inlets for the cooling chambers, the cooler itself may be readily constructed. It will be appreciated that more or less than four exemplary cooling chambers may be used if desired. The constant volume cooling and consequent increased efiiciency of compression will be accomplished by the modifiedconstruction of Fig. 4 of the drawings, in the same manner discussed in connection with the preferred embodiment of Fig. l.

I claim as my invention:

1. A gas compression system comprising, in combination, compressor means for compressing gas from an initial pressure to a higher discharge pressure, said means producing a modulated cyclical flow of gas at the higher pressure, gas cooling means having a volume equal to the volume of gas in one cycle of the modulatedflow of gas at the discharge conditions of said compressor means, said gas cooling means having an inlet in communication with said compressor means and having an outlet, and valve means associated with said inlet and outlet for maintaining the gas in one cycle of gas flow in said cooling means at constant volume during the cooling thereof, said valve means being adapted to permit discharge from said cooling means of the gas in said one cycle of gas Vol. of unswopt cylinder flow and entry of gas in the succeeding cycle of gas flow upon discharge of the latter from said compressor means.

2. A gas compression system comprising, in combination; a gas compressor capable of discharging ansequential flow of uniform, distinct masses of gas; a cooler having a volume equal to the discharge volume of one of said masses of gas, means for conducting the gas discharged by said compressor to said cooler, outlet means for conducting ,the gas' from said cooler, valves associatedwith each of said gas conducting means for retaining each of said masses of gas within said cooler in sequence, and means actuated by said compressor for rendering said cooler effective only when said valves retain one of said masses of gas in said cooler so that each of said masses of gas is cooled at constant volume.

3. A multiple stage gas compressor comprising, in combination, a first cylinder having a reciprocable piston and having inlet and outlet valve means adjacent the upper end of said cylinder, a second cylinder having a gas communication passageway from one of its ends to the upper end portion of said first cylinder and having inlet and outlet valve means adjacent its other end, a floating piston positioned in said second cylinder for reciprocation therein, said piston having an upper and lower working surface at its respective ends, an elastic spring mounted on said second cylinder for resiliently biasing said floating piston toward the valve means of said second cylinder, and power driven means for reciprocating said piston in said first cylinder.

.4. A gas cooler for use with a pressure modulated source of compressed gas comprising, in combination, side and end walls defining a cylindrical gas chamber, said walls having an interior cavity for the circulation of cooling water therein, said walls also having an inlet port and an outlet port adjacent opposite ends of said chamber, check valve means associated with the inlet port to permit gas flow inwardly of said chamber, check valve means associated with the outlet port to permit gas fiow outwardly of said chamber, a series of stationary semicircular fins in spaced, alined relation in said chamher, said fins being in heat transfer contact with said side walls, a hollow spindle mounted for rotation on the longitudinal axis of the gas chamber, said spindle having coupling means thereon for the passage of cooling water through the center thereof, a series of movable, semicircular fins mounted on said spindle in spaced, alined relation for circular bodily rotation into and out of interleaved alinement with said series of stationary fins, said chamber having a volume equal to the volume of gas in one cycle of modulation of the gas at intake conditions, and means for rotating said movable fins into alinement with said stationary fins during entry of gas to said chamber and out of alinement with said stationary fins for constant volume cooling of gas in the chamber.

5. A two stage gas compressor, comprising, in combination, low pressure cylinder means including inlet and outlet valves adjacent its upper end portion, high pressure cylinder means in coaxial abutting relationship at its lower end with the upper end of said low pressure cylinder means, said high pressure cylinder means including inlet and outlet valves adjacent the upper end of said high pressure cylinder, a reciprocable piston in said low pressure cylinder means, means including a crankshaft for reciprocably driving said piston, a piston having closed upper and lower ends in said high pressure cylinder, and means for resiliently biasing said high pressure piston in a direction toward said high pressure valve means, the lower end of said high pressure cylinder means being open to the interior of said low pressure cylinder means so that variations in gas pressure in the latter are applied to the closed lower end of said high pressure cylinder.

6. A gas cooler for use with a reciprocating piston type of gas compressor comprising, in combination, side and end walls defining a cooling chamber, said walls being of double construction for the admission of cooling water therebetween, a plurality of stationary fins positioned in side by side spaced alinement and mounted in heat transfer contact with said walls, a plurality of movable fins positioned in side by side alinement and disposed in alternate series relation with said stationary fins for movement into and out of intermeshing relation to said stationary fins, and means controlled by said compressor for moving said movable fins into said intermeshing relation upon discharge of gas from said compressor and thereafter moving said movable fins out of said intermeshing relation to increase the cooling of discharged gas in said chamber. 2

7. A two stage gas compressor comprising, in combination, first and second gas cylinders positioned in end-toend abutting engagement, said second cylinder being of smaller diameter than said first cylinder and having a cylinder head enclosing the outer end thereof, first and second reciprocable pistons in said first and second cylinders respectively, said first cylinder having inlet and outlet gas passageways adjacent the abutting end, said cylinder head having inlet and outlet gas passageways in communication with the interior of said second cylinder, valve means in each of said passageways for admitting gas from said respective inlet passageways upon reciprocation of said pistons in one direction and discharging gas through said respective outlet passageways upon reciprocation of said pistons in the reverse direction,

said second'piston having a length equal to the length of v head and connected tosaid tensile connector at the other end so that said second piston is resiliently biased toward said cylinder head, the interior of said second cylinder being open to the interior of said first cylinder at their 1 abutting ends so that said second piston is free to project into said first cylinder upon reciprocable movement away from said cylinder head, and crankshaft means for applying a reciprocating motion to said first piston, said second piston having a closed end so that said second piston is actuated by pressure differentials of gas in said first and second cylinders.

8. A gas compression system comprising, in combination, a two stage gas compressor having a low pressure cylinder and a high pressure cylinder, each of said cylinders having a piston adapted to be reciprocably actuated in a compression stroke and a suction stroke, each of said cylinders also having intake and discharge means, a cooler having a plurality of gas cooling chambers, each of said chambers having an inlet and outlet and also having valve means associated with the inlet and outlet respectively, said valve means being adapted to permit a flow of gas into and out of each of said chambers upon discharge of gas during the compression stroke of said compressor pistons and to close upon completion of such discharge by the compressor, the inlet of one of said chambers being in communication with the discharge means of said low pressure compressor cylinder, the inlet of a second one of said chambers being in communication with the discharge means of said high pressure compressor cylinder, each of said chambers having a volume equal to the respective volumesof gas discharged upon the compression stroke of the low and high pressure piston, a third one of said cooling chambers having its inlet in communication with the outlet of the one of said chambers in communication with the low pressure cylin der, said third one of said cooling chambers having a volume equal to the volume of gas delivered to the same from said preceding cooling chamber on each compression stroke of the low pressure piston, an interstage gas conduit means interconnecting the outlet of said third one of the cooling chambers with the intake of said high pressure cylinder, and means operatively associated with said compressor for reducing the cooling capacity of said chambers during the discharge of gas by said compressor cylinders.

9. In a gas compression system having means for producing a discharge of compressed gas in a modulated flow, a cooler for the compressed gas comprising, in combination, means defining a chamber for reception of said compressed gas, means for cooling said chamber, said chamber having a volume equal to the volume of compressed gas discharged by said compressing means in one cycle of modulated flow at the compressor discharge temperature and pressure conditions of the compressed gas, means for interrupting the said flow of compressed gas to hold the volume of gas discharged in one cycle of said modulated flow in the said chamber until the volume of gas in the next succeeding cycle enters said chamber so that each discharged volume of gas is cooled at substantially constant volume.

10. A gas compression system comprising, in combination, a gas compressor capable of' discharging compressed gas in a modulated flow in a series of cycles, a cooler for the compressed gas having means defining a chamber for reception of the compressed gas, said chamber having a volume equal to the volume of the compressed gas in one of said cycles at the discharge pressure and temperature conditions of said compressor, inlet means for said first chamber for conducting compressed gas from said compressor to said chamber, outlet means for conducting gas from said chamber, valve means in said inlet and outlet means for retaining the compressed gas in one cycle of said modulated flow in said chamber until the volume of gas in the next succeeding cycle of modulated flow enters said chamber, means for cooling said chamber, and means for controlling said cooling means to increase the cooling capacity of said cooling means when compressed gas is retained in said chamber and reducing the cooling capacity upon entrance and exit of compressed gas so that said gas is cooled at substantially constant volume.

11. A gas compression system as claimed in claim 1 in which said compressor means comprises a cylinder and piston and said cooling means comprises a series of cooling chambers, the inlet for said cooling means being a series of individual inlets, one for each chamber and positioned relative to each other along the length of said cylinder for receiving compressed gas at a series of increasing discharge pressures, said chambers having means for sequential flow of gas from one chamber to another, the outlet of said cooling means being in communication with the last one of said series of said chambers positioned at the high-pressure end of said cylinder, the volume of said cooling means being the combined volume of said chambers and equal to the volume of gas discharged by said compressor means in one cycle of gas flow to said series of chambers at the respective compressor discharge conditions existing at said inlets, the relative volume of said chambers being such that a charge of cooled gas in a preceding chamber when added to that of the next chamber raises the pressure in the latter to substantially the highest inlet pressure of the preceding chamber, the positions of said inlets along said cylinder being such that the volume of gas in the unswept portion of said cylinder beyond a respective inlet is equal to the volume of the remaining one of said series of chambers at the respective inlet conditions of the References Cited in the tile of this patent UNITED STATES PATENTS 252,921 Allen Jan. 31, 1882 699,288 Cowles May 6, 1902 1,008,519 Barr Nov. 14, 1911 1,701,777 Jensen Feb. 12, 1929 2,119,201 Cook May 31, 1938 2,159,463 Voorheis May 23, 1939 2,186,492 Paget Jan. 9, 1940 

